FIG. 1 is a diagram of the power supply circuit for a conventional discharge lamp. The discharge lamp, given reference L, is connected in series with a high voltage module HT for generating a high voltage trigger pulse, and it is voltage triggered by a DC/AC converter (constituted by a DC/AC H-bridge) downstream from a DC/DC converter including a transformer and receiving as its input the (12 V) voltage provided by the vehicle battery B.
The DC/DC converter generates all of the voltages required other than that of the trigger pulse. In particular, it must be capable of providing a high voltage of 500 V for several milliseconds for starting purposes.
The transformers that have been used up to now in such DC/DC converters powering the discharge lamps of motor vehicle headlights have therefore been relatively bulky.
Unfortunately, it is presently desired to reduce the bulk of discharge lamp power supply circuits so as to enable them to be housed completely within headlights, whereas until now the converters of such power supply circuits have been outside the corresponding headlights.
U.S. Pat. No. 4,873,757 discloses transformers of small dimensions in which the windings are constituted by a multilayer printed circuit and in which the ferrites are constituted by a pair of E-shaped ferrites that are closed one on the other with their branches passing through openings in the multilayer circuit.
The ferrites and the multilayer circuit are applied to a printed circuit. To this end, the ferrites are held in metal banding which surrounds them in part and which is bonded at two points to the printed circuit. The metal banding serves to ground the ferrites.
Such a transformer is not always satisfactory.
In particular, the ferrites tend to heat up considerably, thereby making that type of transformer incompatible with certain applications.